Cleans up code associated with callbacks
Cleans up code associated with callbacks

- Replaces usage of the local callback() func with lodash.noop
- Renames callback arguments to confirm with Google style guide

JustinBeckwith/google-auth-library-nodejs,JustinBeckwith/google-auth-library-nodejs,tbetbetbe/google-auth-library-nodejs,JustinBeckwith/google-auth-library-nodejs,authbox-lib/google-auth-library-nodejs,moander/google-auth-library-nodejs,googleapis/google-auth-library-nodejs,JustinBeckwith/google-auth-library-nodejs,googleapis/google-auth-library-nodejs,murgatroid99/google-auth-library-nodejs,ofrobots/google-auth-library-nodejs,andrezzoid/google-auth-library-nodejs,mlmorg/google-auth-library-nodejs